Parts made from Si.sub.3 N.sub.4 are expected to find extended use in high temperature applications as, for example, in the hot parts of gas turbine engines or other load-carrying elements. To make such parts readily usable there must be a suitable composition for joining these parts to make composite structures that will maintain their integrity in use and under the stresses to which the composite may be subjected. Such compositions must serve to join the said Si.sub.3 N.sub.4 pieces securely without detrimentally affecting the pieces joined by the composition.
The .beta.'-Y.sub.2 Si.sub.2 O.sub.7 --Y.sub.3 Al.sub.5 O.sub.12 compatibility tetrahedron establishes a group of compositions that it was hoped could be usable as a brazing material. Compatibility relationships in the Y--Si--Al--O--N system are described in a report to NASA, Report No. NASA CR 159675, dated September 1979 and also in a paper by Layden, No. 61-BN-79F, presented at the Fall meeting in October 1979 to the American Ceramic Society.